Method and apparatus for adaptive transmit power control

ABSTRACT

Systems and methods for dynamically adjusting transmit gain in a transceiver. The gain is adjusted in order to provide the maximum gain. The amount of distortion is measured. The gain is increased until the distortion reaches a predetermined limit. The gain of several components can be adjusted independently.

TECHNICAL FIELD

The disclosed method and apparatus relate to radio frequencytransmitters, and more particularly to methods and systems forcontrolling the power level of transmissions from a radio frequencytransmitter.

BACKGROUND

Error free transmission of information is important in thecommunications industry today. In order to effectively transmitinformation modulated on radio frequency signals either over the air oron a medium such as a coaxial cable, it is helpful to properly set thepower level at which modulated radio frequency signals are to betransmitted. The effective use of transmission power is the focus ofmuch attention. Communications engineers are frequently concerned withis maximizing the amount of power used to transmit signals withoutcausing distortion that will cause errors in the demodulation of data onthe receiving side of the communications channel. Another concern issetting the desired amount of transmit power to the level necessary toensure that the intended receivers receive the signals with sufficientpower to accurately demodulate the information transmitted, but with nomore power than is necessary. Accurately determining the amount of powerthat can be transmitted with an acceptable level of distortion allowsthe greatest transmit power range and the greatest data throughput.

In some systems, a closed loop power control system is used. Such closedloop power control systems require the receiver to provide feedbackregarding the receiver's ability to accurately demodulate theinformation that is being transmitted. Such closed loop power controlsystems are relatively slow and require the receiver to demodulate thetransmitted information before such feedback can be provided.

In addition to closed loop feedback control systems, transmitters aretypically calibrated prior to being sent out to the field. Thecalibration is an attempt to determine the dynamic range of thetransmitter and determine the particular output levels at whichdistortion will occur and to determine the amount of loss that thesignal will incur prior to being transmitted.

FIG. 1 is a simplified block diagram of a transmission section 100 of atransmitter. The maximum power that a transmitter can transmit istypically determined at the time the circuit is designed. Once thecircuit is manufactured, the circuit is tested to determine thecharacteristics of the particular components that comprise thetransmission section 100. The transmission section 100 is connected to atest load that simulates the conditions under which the transmissionsection 100 will be operating when put to use in the field. Thetransmission section 100 is placed in calibration/test mode by thecombination of a receive/transmit (R/T) switch 102 and a calibrationswitch 112. In calibration/test mode, the R/T switch 102 disconnects apower amplifier (PA) 104 from a filter 106. In addition, the calibrationswitch 112 is closed to connect the output of the PA 104 to the input ofa detector 114. The output of the PA 104 is also connected to a nominaltest load 116 having a resistance that is equal to the impedance of themedium into which the transmission is to be launched (e.g., 75 ohms).Therefore, when the switch 112 is closed, the amount of power output bythe PA 104 is measured by the detector 114.

A test signal is injected into the PA 104. A measurement made by thedetector 114 on the test signal is reported to a PA controller 118. ThePA controller 118 adjusts the gain of the PA 104 until the signal levelis at a target value. The target value is determined based upon anestimate of a set of factors. These factors include the errors thatmight be present in the detector 114, any uncertainty in the level atwhich the PA 104 will begin to compress/distort the signals beingamplified and the amount of distortion and attenuation due to the outputfilter 106 and the impedance of the load (not shown) coupled to theoutput port 108. Once the proper gain is determined for the PA 104, theunit is ready to be used in the field.

Accounting for all of the uncertainties associated with factors notedabove requires a relatively large safety margin. That is, thetransmission section 100 may need to operate at 3 dB, or more, abovewhat is determined by the test procedure to be at the point at whichinformation delivered to the load can be accurately demodulated.Accordingly, the transmitter will deliver enough power to meet thedesired target in the majority of cases, but with more power than mightbe appropriate for the average situation. This is done in order toensure that the power settings will provide a reliable signal(acceptable receive power) in the majority of situations. Eventransmitting with a safety margin of 3 dB (i.e., doubling the targetlevel output power) may not be sufficient to ensure that the targetlevel output power will actually be delivered in all cases. The marginmust be selected such that when the unknown factors noted above are attheir worst case values, every unit (or at least every unit minus anegligible number of outlier units) will be able to deliver a signalthat has an acceptable power level without excessive distortion.

While the margin noted above is required in order to ensure properoperation in nearly all cases, transmitting with such a margin is notnecessary in most cases. Transmitting with a margin that is greater thannecessary in most cases means that the DC power is significantly higherthan necessary in most cases (i.e., nearly double that required). Yet,the resulting operation may still be sub-optimal in outlying cases dueto the uncertainties that exist from unit to unit and situation tosituation. In order to optimize the power level of transmissions,extensive work is done in the laboratory to obtain statistics anddetermine the most efficient and effective margin possible. Even withsuch work, a compromise is required. That is, a balance must be struckbetween providing more power than is optimal in some cases under theassumption that the more power will be necessary than then is actuallythe case and transmitting with less power than is optimal in cases inwhich these factors require more power than is assumed.

In addition to the above situations, in systems that use a closed looppower control system, the path between a transmitter and one receivermay have more loss than the path to several other receivers. In thiscase, the transmitter will be driven to transmit more power than isrequired for the receivers communicating over the low loss paths.Transmitting at the higher power level can cause distortion in thetransmitter that results in errors occurring in the informationtransmitted. Therefore, a relatively large number of receivers willsuffer because of the needs of one receiver.

Accordingly, there is presently a need for a method and apparatus thatcan more efficiently and effectively determine the amount of power withwhich a transmitter should transmit signals to ensure that a targetoutput power will be delivered with an acceptable level of distortion.

SUMMARY

Various embodiments of the disclosed method and apparatus for deliveringa target output power are presented. Some of these embodiments aredirected toward systems and methods for adaptively determining theamount of transmit power required to account for several factors. Thesefactors include: (1) errors that might be present in a detector used todetect output power, (2) uncertainty in the level at which a poweramplifier used in the system will begin to compress or distort thesignals being amplified and (3) the amount of distortion and attenuationthat is due to output filters and the impedance of the load coupled tothe output port of the transmitter.

In accordance with one embodiment of the disclosed method and apparatus,output power from the transmission section of a transceiver is measuredduring actual transmission to a load, such as a live network. Aloop-back path is provided between the output of a power amplifier (PA)and the input of a low noise amplifier (LNA). Accordingly, output poweris provided from the PA to the receiver section of the transceiver. Inone embodiment, a test signal is provided and transmitted into theactual load in the field during designated times set aside by thenetwork manager. In another embodiment, the measurements are made duringactual operation with live data (i.e. data intended to be received by areceiver).

The receiver section of the transceiver evaluates the transmissionsignal. In one embodiment, the evaluation includes measuring thetransmit modulation error ratio (TxMER). Alternatively, compression ofthe peak power level measured to evaluate the transmission signal. Again control module performs a procedure that starts at a relatively lowpower level and increases the power level in steps. After eachincremental increase in the power, a measurement is made to ensure thatthere is an acceptable level of distortion to the output signal.Additional adjustments can be made to the input power applied to adigital to analog converter (DAC) that precedes the PA. That is, thedigital input to the DAC can be adjusted to ensure that the input to theDAC is at the optimal level (i.e., that input of the PA is as high aspossible with the distortion generated by the DAC maintained at anacceptable level). In addition, in one embodiment, a pre-amplifier(pre-amp) amplifies the output of the DAC prior to the signal beinginput to the PA. In one such embodiment, the gain of the pre-amp is alsooptimized.

In one embodiment, the peak amplitude is monitored. Both amplitude andphase compression in the peak amplitude are monitored and used as ametric of the amount of distortion present in the output signal. Theamount of distortion is used to determine the proper amount of gain foreach component of the transmission path.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed method and apparatus, in accordance with one or morevarious embodiments, is described with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict examples of some embodiments of the disclosed method andapparatus. These drawings are provided to facilitate the reader'sunderstanding of the disclosed method and apparatus. They should not beconsidered to limit the breadth, scope, or applicability of the claimedinvention. It should be noted that for clarity and ease of illustrationthese drawings are not necessarily made to scale.

FIG. 1 is a simplified block diagram of prior art transceiver.

FIG. 2 is a simplified block diagram of a transceiver in accordance withone embodiment of the presently disclosed method and apparatus.

FIG. 3 is a simplified functional block diagram of a control andmeasurement module (CMM).

FIG. 4 is a simplified block diagram of the transmit block.

FIG. 5 is a flowchart of the method performed by the CMM to maximize theoutput of each component while ensuring that the amount of distortion tothe output signal remains within a predetermined limit and accuratelymeasure the output power provided to an actual load.

The figures are not intended to be exhaustive or to limit the claimedinvention to the precise form disclosed. It should be understood thatthe disclosed method and apparatus can be practiced with modificationand alteration, and that the invention should be limited only by theclaims and the equivalents thereof.

DETAILED DESCRIPTION

FIG. 2 is a simplified block diagram of a transceiver 200 in accordancewith one embodiment of the presently disclosed method and apparatus. Thetransceiver 200 includes a Control and Measurement Module (CMM) 202. TheCMM 202 is coupled to a transmission (Tx) block 204. The CMM 202provides digital signals 205 that are to be transmitted to the Tx block204. The amplitude of the digital signals 205 are adjustable by the CMM202. In accordance with one embodiment of the disclosed method andapparatus, the digital signals 205 include test signals at selectedtimes in order to measure the amount of distortion that exists in thetransmitted signal. In an alternative embodiment, the amount ofdistortion present in the transmitted signals is measured directly withdigital signals modulated with “live” data (i.e., data intended for areceiver to which the transceiver is transmitting). The Tx block 204outputs an analog signal to a power amplifier (PA) 206. The CMM 202, theTx block 204 and the PA 206 are part of a transmit chain. The PA 206provides a variable amount of gain to the signal coupled to an outputfilter 208. The gain of the PA 206 is controlled by a PA gain controlsignal 207 coupled to the PA from the CMM 202. The PA 206 is coupled tothe output filter 208 by a receive/transmit (R/T) switch 210. The R/Tswitch 210 is shown in the transmit position. In one embodiment of thepresently disclosed method and apparatus, the R/T switch 210 iscontrolled by a switch control signal 211 from the CMM 202. Thoseskilled in the art will understand that the particular arrangement ofcomponents in the transmit chain may vary significantly. Nonetheless, inaccordance with the disclosed method and apparatus, the gain of one ormore components is controlled in order to set the transmit power levelof the output. The particular example provided herein is merely oneimplementation a transmit chain of the disclosed method and apparatus.

In one embodiment of the disclosed method and apparatus, the output ofthe PA 206 is coupled to a loop-back path 226. In accordance with oneembodiment, the loop-back path 226 includes a first isolation resistor212, a test/calibration (T/C) switch 214, and a second isolationresistor 216. The first isolation resistor 212 shunts some of the outputpower to the T/C switch 214. In accordance with one embodiment of thedisclosed method and apparatus, the T/C switch 214 is controlled by aswitch control signal 215. The second isolation resistor 216 couples theoutput of the T/C switch 214 to the input of a low noise amplifier (LNA)218 when the T/C switch 214 is closed. Thus, a loop-back signal isderived from looping back a portion of the output of the PA 206 andcoupled to the input of the LNA 218.

The output of the LNA 218 is coupled to a receive block (Rx) 220. The Rxblock 220 converts the analog output from the LNA 218 to a digitaloutput signal 222. The digital output signal 222 from the Rx block 220is coupled to an input to the CMM 202. Note that the input to the LNA218 is disconnected from the filter 208 when the R/T switch 210 is intransmit position.

In an alternative embodiment, the R/T switch 210 leakage when operatingin transmit mode forms the loop-back path. That is, there is sufficientleakage through the switch 210 when the switch 210 is in transmitposition to allow sufficient power in the transmit signal to be coupledfrom the output of the PA 206 to the input of the LNA 218 to serve as aloop-back path and yet provide necessary isolation between the transmitand receive sections of the transceiver 200. Accordingly, in thisembodiment, there is no need for the isolation resistors 212, 216 andthe loop-back switch 214.

In accordance with one embodiment of the presently disclosed method andapparatus, the CMM 202 is a digital signal processor (DSP). Informationto be transmitted is provided to the CMM 202. The CMM 202 will modulatethe information and output that information to the Tx block 204 as adigital signal. In addition, in accordance with one embodiment of thedisclosed method and apparatus, the CMM 202 outputs a digital to analogconverter (DAC) and pre-amp gain control signal 224 to the Tx block 204.

FIG. 3 is a simplified functional block diagram of the CMM 202. Inaccordance with one embodiment of the disclosed method and apparatus,the CMM 202 includes a CMM processor 301, a configuration control module302, a distortion measurement module 304 a gain control module 306 and atransmission modulation and upconversion module 308. The configurationmodule 302 provides the switch control signals 211, 215 used toconfigure the switches 210, 214. In an alternative embodiment of thedisclosed method and apparatus, the switches 210, 214 are controlleddirectly by the CMM processor 301.

The distortion measurement module 304 receives the digital output signal222 from the Rx block 220. The distortion measurement module 304analyzes the digital output signal 222 and determines whether thedistortion present in the digital output signal 222 is above anacceptable distortion level. Alternatively, the digital output signal222 is directly coupled to the CMM processor 301. The CMM processor 301directly determines whether the amount of distortion present in thedigital output signal 222 is above an acceptable distortion level.

In accordance with an alternative embodiment of the disclosed method andapparatus, the output signal 222 from the Rx block 220 is an analogsignal. In one such embodiment, the analog signal is coupled directly tothe CMM processor 301. The CMM processor 301 digitizes the output signal222 from the Rx block 220 and determines whether the amount ofdistortion present in the output signal 222 is above an acceptabledistortion limit.

The gain control module 306 controls the gain of transmit components,including the pre-amp 306 and the PA 206 based on input provided to thegain control module 306 from the CMM processor 301. In addition, the CMMprocessor 301 and/or the transmission modulation and upconversion module308 constitute a transmission component by which the gain of the digitalsignal 205 can be adjusted. In accordance with one embodiment, the CMMprocessor 301 determines the amount of gain to be set in the PA 206 andpre-amp 306 based on the amount of distortion measured by the distortionmeasurement module 304. In an alternative embodiment of the disclosedmethod and apparatus, the gain control module 306 is directly coupled tothe distortion measurement module 304. The CMM processor 301 alsodetermines the amount of gain to applied to the digital signal 205 basedon the amount of distortion measured by the distortion measurementmodule 304.

It will be clear to those skilled in the art that each of the moduleswithin the CMM 202 may be implemented by a software module executed by aprocessor, such as a digital signal processor. Alternatively, one ormore of the modules can be implemented using discrete hardware dedicatedto the function disclosed for the particular module. In yet anotheralternative embodiment, one or more of the modules is implemented as adedicated state machine. In yet another alternative embodiment, one ormore of the modules is implemented as firmware executed by a processoror state machine. In yet another alternative embodiment, one or more ofthe modules within the CMM 202 are implemented as a combination of oneor more of the following: software executed by a processor, firmwareexecuted on a processor or state machine, discrete hardware, or adedicated state machine.

FIG. 4 is a simplified block diagram of the Tx block 204 in accordancewith one embodiment of the presently disclosed method and apparatus. TheTx block 204 comprises a DAC 402, a filter 404 and a pre-amp 406. In oneembodiment of the disclosed method and apparatus, the pre-amp 406 hasvariable gain. The gain control signal provided from the CMM 202controls the gain of the pre-amp 406.

The digital signal output 205 from the CMM 202 to the Tx block 204 isconverted to an analog signal by the DAC 402. The filter 404 reduces anyout of band spurious signals that are generated by the DAC 402. Thepre-amp 406 then amplifies the signals to be output to the PA 206. TheDAC 402, the pre-amp 406, and the filter 404 all contribute to the noisethat is generated by the Tx block 204. The noise is a function of thelinearity of the components and the signal levels that are applied toeach component of the Tx block 204. In accordance with one embodiment ofthe disclosed method and apparatus, the CMM 202 controls the input levelto the DAC 402 and the amount of gain applied by the pre-amp 406 inorder to maximize the output transmit power of the transceiver 200 whileensuring that there is no more than a predetermined maximum amount ofdistortion.

FIG. 5 is a flowchart of the method performed by the CMM 202 of thetransceiver 200 to maximize the output of each component while ensuringthat the amount of distortion to the output signal remains within apredetermined limit. In accordance with the example presented in FIGS.2-4, the process shown in FIG. 5 will be implemented for the input tothe DAC 402, the gain of the pre-amp 406 and the gain of the PA 206.Those skilled in the art will understand that this process can beimplemented with respect to any component of the system for which thegain can be adjusted. In accordance with one embodiment of the disclosedmethod and apparatus, each of these will be adjusted independently.Alternatively, one or some combination of some of these components willbe adjusted together. In yet another alternative embodiment, the gain ofonly one or some combination of less than all components are adjusted.

In accordance with one embodiment, the process is first implemented forthe digital input level to the DAC 402. The system is initialized bysetting the R/T switch 210 to the transmit position (see FIG. 2). TheT/C switch 214 is closed. The input to the DAC 402, the gain of thepre-amp 406 and the PA 206 are each set to an initial setting that doesnot contribute to the distortion (STEP 502). Accordingly, the gain isinitially set to a level that is in the center of the operating range ofeach component. It should be noted that if the signal levels of theinputs to and outputs from those components are essentially near thecenter of the operating range, they typically will contribute minimallyto the distortion of the output signal. Accordingly, the signals areamplified to a level that is known to have an minimum amount ofdistortion.

In accordance with one embodiment of the disclosed method and apparatus,the fact that the amount of distortion is minimized can be verifiedduring the process by adjusting the gain of the pre-amp 406 up slightlyfrom the initial gain setting. A determination can then be made as towhether any additional distortion is added to the loop back signal asmeasured by the CMM 202. The gain of the pre-amp 406 can then beadjusted down slightly from the initial setting. The output can then bechecked again to determine whether any additional distortion occurs tothe loop back signal. It should be noted that the amount of distortionshould remain essentially constant in that part of the operating rangewhere minimum distortion occurs. A similar verification can be performedfor the digital input level to the DAC 402 and for the gain of the PA206.

In accordance with one embodiment, once the levels have beeninitialized, the CMM 202 will measure the amount of distortion that ispresent in the loop back signal output from the Rx block 220 to the CMM202 (STEP 504). In accordance with one embodiment of the disclosedmethod and apparatus, the transceiver 200 is transmitting into anoperational load, such as an active network (i.e., a network that has atleast one active node communicating on the network) when the measurementis taken. If the distortion is less than a predetermined limit (STEP506), then the level of the digital signal input to the DAC 402 isincreased (STEP 508). In accordance with one embodiment, it can beassumed that when initially set essentially to the center of theoperating range, the minimum amount of distortion will be introduced byeach component of the transceiver 200 (i.e., the signal will beamplified to a signal level that is known to be acceptable). Therefore,level of the digital signal input to the DAC 402 is increased (STEP508). The CMM 202 then makes another measurement of the amount ofdistortion in the loop back signal (STEP 504). This will continuethrough the STEPs 504 through 508 until the amount of distortion in theloop back signal is greater than the predetermined limit (STEP 506).Once the distortion is greater than the predetermined limit (STEP 506),a determination is made as to whether the signal level is below apredetermined threshold (STEP 510). This determination will ensure thatthe reason that the distortion is greater than the limit is because thegain being adjusted is too high. That is, the distortion could begreater than the predetermined limit if the signal level is set too low.Checking that the level is not below a predetermined threshold ensuresthis is not the case. Therefore, if the level of the signal that isbeing analyzed by the CMM 202 is not below the predetermined threshold,then the level of the digital input is decreased (STEP 512). Afterdecreasing the level of the digital input, the process returns to STEP504.

This process is then repeated for the gain of the pre-amp 406 and thegain of the PA 206.

TxMER is the amount of power that is provided by the signal at theintended quadrature amplitude modulation constellation point withrespect to the amount of power at points other than the intendedconstellation point (i.e., the amount of power due to distortion of themodulated signal). In accordance with one embodiment of the disclosedmethod and apparatus, TxMER is used to measure the amount of distortionthat is present in the signal.

In an alternative embodiment, distortion is measured based on the peakamplitude of the signal. Alternatively, the amount of distortion ismeasured based on the peak to average ratio of the signal received inthe CMM 202. Determining the amount of distortion based on the peakamplitude or the peak to average ratio has the advantage of notrequiring demodulation of the signal. In contrast, measuring TxMERrequires demodulation. Therefore, measurements of distortion based onthe peak amplitude or the peak to average ratio can be made much fasterthan measurements based on TxMER.

In accordance with one embodiment, both amplitude compression and phasecompression of the peak amplitude can be measured. Phase compressionoccurs due to phase shifts as a consequence of non-linearities thatoccur as the signal levels rise. Similarly, amplitude compression occurswhen an increase in the amplitude at the input of the component is notlinear with respect to the resulting increase in the amplitude at theoutput of the component. Both amplitude compression and phasecompression are measured by the CMM 202 and used as a measure of theamount of distortion when implementing the process shown in FIG. 5.

In accordance with one embodiment, a test tone having three coherentfrequencies is used to adjust the gain of the components (e.g., the PA206, the pre-amplifier 406 and the DAC 402). In one embodiment, thethree frequencies are each carrier frequencies of an orthogonalfrequency division multiplexed (OFDM) signal upon which test data ismodulated. The CMM 202 outputs the test tone to be applied to the Txblock 204. The process of FIG. 5 is implemented and the gain of each ofthe components is adjusted. The peak amplitude can be measured at thepoint at which each of the frequencies is concurrently at 0 degrees inphase (i.e., when each is at peak amplitude). Any distortion that willoccur will be maximum at that point. If either phase or amplitudecompression is occurring, then the non-linear response can be detectedby measuring the output while the amplitude of the input is increased(or decreased). This non-linear response will be indicative ofdistortion caused by overdriving one of the components. In oneembodiment, several measurements of the distortion are made and averagedto improve the accuracy of individual measurements.

Since the PA 206 is connected to the operational load during theadjustment of the gain of each of the transmit components, the actualoperational conditions are taken into account in making the gainadjustments. That is, in systems in which the output of the PA 206 iscoupled to a load other than the actual operational load, the amount ofdistortion can change significantly from that which occurs under actualconditions. Furthermore, in many systems the particular nature of theload will vary significantly from one operational setting to another.That is, in the case in which the transceiver is a set top boxcommunicating over a home entertainment network, such as a networkoperating in accordance with the well-known MoCA (Multimedia over CoaxAlliance) standard, the load conditions of one home will besignificantly different from the load conditions of another home.Therefore, adjustments made without taking the particular loadconditions into account will require a relatively large margin. That is,in many situations, the gain will be set significantly higher thanoptimal, since the particular conditions of some homes into which thedevice is installed will be better than the average assumed when settingthe gain. Even more to the point, the gain cannot even be set with anassumption of “average load conditions”, since a significant percentageof homes will have conditions that are substantially worse than average.Using the actual output load that is used during normal operation whenmaking gain adjustments ensures that the gain is accurately set foractual operational conditions. This is the case whether the input signalis a test tone or an actual signal to be transmitted. In one embodiment,gain adjustments are made on a continual basis with actual data beingtransmitted. Alternatively, the gain adjustments are made duringdesignated transmission test slots (i.e., slots when test tones can betransmitted without interfering with the operation of the network intowhich the test tones are being transmitted). Nonetheless, the load onthe transceiver 200 will be the actual operating load.

In addition to adjusting the gain under actual load conditions, the gaincan be adjusted to account for changes in the operating conditions,including changes in temperature, the number of nodes on the network,changes in the power supply, etc. By adjusting the load under actualconditions, difficult statistical analysis that is currently used todetermine the optimum operating gain for transmission, can beeliminated. That is, determining the amount of gain to be applied byeach component requires several complex models to be created todetermine what the worst case load will look like and at what point tocompromise between higher output power and greater distortion under loadconditions that, while unlikely to occur frequently, are certain tooccur from time to time. That is, a compromise will always need to bemade between having a limited number of installations encounter outputpower levels that are insufficient to allow accurate demodulation by allreceivers and setting the gain of the transmitters too high in order toensure that there is sufficient power to allow receivers to demodulatedata accurately under bad conditions.

In one embodiment, the transmit signal can be intentionallypre-distorted (e.g., by adding third order, complex phase and amplitudecorrections) to compensate for distortion that will occur through thetransmission components. In one embodiment, a filter with adaptive tapweights using a least mean squares (LMS) algorithm can assist inmitigating distortion at higher output levels to extend the range of thetransmission components.

The isolation resistors 212, 216 provide isolation that reduces theloading of the PA 206 when the T/C switch 214 is closed. Alternatively,the T/C switch is eliminated. The PA 206 output is coupled directlythrough the isolation resistors 212, 216 to the LNA. The resistors 212,216 reduce the loading on the PA 206 and direct as much energy aspossible to the load connected to the RF output 209. In yet anotherembodiment, the leakage through the R/T switch 210 provides sufficientsignal to the input of the LNA 218 that no other path from the output ofthe PA 206 to the LNA 218 is required.

Although the disclosed method and apparatus is described above in termsof various examples of embodiments and implementations, it should beunderstood that the particular features, aspects and functionalitydescribed in one or more of the individual embodiments are not limitedin their applicability to the particular embodiment with which they aredescribed. For example, while peak amplitude level, peak to averageratio and TxMER are disclosed as convenient measures of distortion, itwill be clear to those skilled in the art that other measures ofdistortion can be used to assist in the adjustment of the gain of thetransmit components.

Furthermore, the particular number, type and combination of transmissioncomponents for which gain is adjusted and the order in which the gain isadjusted can vary in alternative embodiments of the disclosed method andapparatus.

Still further, while the CMM 202 is disclosed as measuring thedistortion and controlling the gain, these functions can be performed bydiscrete components, a dedicated digital signal processor, a statemachine or other circuitry that is designed to perform the functionsdisclosed above.

Further yet, the particular nature of the test signal used to drive thetransmission components during gain adjustment can vary. It will beunderstood by those of ordinary skill in the art that the test signalcan be one of a very large number of types of signals, as long as theamount of distortion in the signal can be detected by the receiversection of the transceiver 200.

In yet another alternative embodiment, a separate loopback receiver canbe provided that is dedicated to receiving the looped back signal andmeasuring the distortion.

Thus, the breadth and scope of the claimed invention should not belimited by any of the examples provided in describing the abovedisclosed embodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide examples of instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of thedisclosed method and apparatus may be described or claimed in thesingular, the plural is contemplated to be within the scope thereofunless limitation to the singular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are describedwith the aid of block diagrams, flow charts and other illustrations. Aswill become apparent to one of ordinary skill in the art after readingthis document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is:
 1. A transceiver comprising: a variable gain poweramplifier (PA), the PA configured to receive a signal to be transmitted,and provide gain to the signal to be transmitted; a loop-back circuitcomprising: a first terminal and a second terminal, the first terminalcoupled to an output of the PA; a first resistor having a first andsecond terminal, the first terminal of the first resistor coupled to theoutput of the PA; a loop-back switch having a first and second terminal,the second terminal of the first resistor coupled the first terminal ofthe loop-back switch; and a second resistor having a first and secondterminal, the first terminal of the second resistor coupled to thesecond terminal of the loop-back switch and the second terminal of thesecond resistor coupled to an input to a low noise amplifier (LNA); anda control and measurement module that is: coupled to the PA and to anoutput of the loop-back circuit; and configured to: provide the signalto be transmitted to the PA; measure whether distortion to the signalcoupled from the output of the loop-back circuit is above an acceptablelimit; if the amount of distortion is below the acceptable limit,provide a signal to the PA to increase the gain provided by the PA; andif the amount of distortion is above the acceptable limit, reduce thegain provided by the PA.
 2. The transceiver of claim 1 furthercomprising: a) a transmit block, wherein signals coupled from thecontrol and monitor measurement module to an input of the PA are coupledthrough the transmit block; and b) the LNA wherein signals coupledbetween the second terminal of the loop-back circuit and the control andmeasurement module are coupled through the LNA.
 3. The transceiver ofclaim 2, further comprising a receive block, wherein signals coupledbetween the LNA and the control and measurement module are coupledthrough the receive block.
 4. The transceiver of claim 3, wherein: thereceive block includes a digital to analog converter (DAC); the controland measurement module is configured to: control the gain of digitalinputs to the DAC; set the gain of the digital inputs to the DACindependent of the PA based on the determination of whether thedistortion to the signal coupled from the output of the loop-backcircuit is above the acceptable limit, wherein: if the distortion to thesignal coupled from the output of the loop-back circuit is above theacceptable limit, gain of the digital inputs to the DAC is decreased;and if the distortion to the signal coupled from the output of theloop-back circuit is below the acceptable limit, gain of the digitalsignal is increased.
 5. The transceiver of claim 2, further comprising atransmit/receive (T/R) switch having a first input/output (I/O)terminal, a second I/O terminal and a common terminal, the first I/Oterminal coupled to the output of the PA, the second I/O terminalcoupled to an input of the LNA and the common terminal switchable tomake connection with either the first I/O terminal or the second I/Oterminal and wherein the loop-back circuit is formed by the leakage fromthe first I/O terminal to the second I/O terminal between the output ofthe PA and the input of the LNA.
 6. The transceiver of claim 2, wherein:the transmit block includes a pre-amplifier; the control and measurementmodule is configured to: set gain of the pre-amplifier independent ofthe PA based on the determination of whether the distortion to thesignal coupled from the output of the loop-back circuit is above theacceptable limit, wherein: if the distortion to the signal coupled fromthe output of the loop-back circuit is above the acceptable limit, gainprovided by the pre-amplifier is increased; and if the distortion to thesignal coupled from the output of the loop-back circuit is below theacceptable limit, gain provided by the pre-amplifier is decreased. 7.The transceiver of claim 1, wherein the output of the PA is coupled toan operational load.
 8. The transceiver of claim 7, wherein theoperational load is an active network.
 9. The transceiver of claim 7,wherein the control and measurement module is configured to provide atest signal to the PA to be transmitted during times at whichtransmission of test signals will not interfere with operations of thenetwork.
 10. The transceiver of claim 7, wherein the control andmeasurement module is configured to: (i) receive information intended tobe transmitted to a receiver over the network; (ii) modulate theinformation; and (iii) couple the modulated information to the PA. 11.The transceiver of claim 1, wherein the distortion measurement comprisesa measurement of the amount of amplitude compression in the peakamplitude of a loop-back signal.
 12. A method for adjusting the gain ofa transmitter, the method comprising: amplifying a transmit signal withan adjustable gain power amplifier (PA); measuring the amount ofdistortion in a loop-back signal while transmitting the amplifiedtransmit signal to an operational load, wherein: the loop-back signal isderived from the transmit signal; and the loop-back signal is coupledfrom the output of the PA to the input of a low noise amplifier (LNA) bya loop-back circuit; the output of the LNA is coupled to a distortionmeasurement module that is configured to determine whether thedistortion in the loop-back signal is less than a limit; if the amountof distortion that is measured is less than the limit, increasing thegain of the PA, otherwise decreasing the gain of the PA; and derivingthe loop-back signal from leakage of a transmit/receive switch intransmit position.
 13. The method of claim 12, further includingperforming the amplifying, the measuring, and the increasing for eachcomponent of a transmit chain of the transmitter for which gain of thecomponent can be adjusted.
 14. The method of claim 12, further includingtransmitting the transmit signal to an operational load while measuringdistortion on the loop-back signal.
 15. The method of claim 12, whereinthe transmit signal is initially amplified to a level that is known tohave an acceptable amount of distortion.
 16. The method of claim 12,wherein the distortion measurement is made based on measurements of apeak amplitude of the loop-back signal.
 17. The method of claim 12,wherein the distortion measurement is made based on measurements of apeak to average ratio of the loop-back signal.
 18. The method of claim12, wherein the distortion measurement is made based on amplitudecompression in the peak amplitude of the loop-back signal.
 19. Themethod of claim 12, wherein the distortion measurement is made based onboth phase compression and amplitude compression in the peak amplitudeof the loop-back signal.
 20. The method of claim 12, wherein thedistortion measurement is made based on transmit modulation error rate(MER) for the loop-back signal.
 21. The method of claim 19, wherein thetransmit signal is a test tone.
 22. The method of claim 21, wherein thetest tone is an orthogonal frequency division multiplexed (OFDM) signalcomprising a plurality of carriers upon which test data is modulated.23. The method of claim 19, wherein live transmit signals modulated withinformation intended for reception by a receiver.
 24. A transceivercomprising: a variable gain power amplifier (PA), the PA configured toreceive a signal to be transmitted, and provide gain to the signal to betransmitted; a loop-back circuit having a first terminal and a secondterminal, the first terminal coupled to an output of the PA; a controland measurement module that is: coupled to the PA and to an output ofthe loop-back circuit; and configured to: provide the signal to betransmitted to the PA; measure whether distortion to the signal coupledfrom the output of the loop-back circuit is above an acceptable limit;if the amount of distortion is below the acceptable limit, provide asignal to the PA to increase the gain provided by the PA; and if theamount of distortion is above the acceptable limit, reduce the gainprovided by the PA; a transmit block, wherein signals coupled from thecontrol and monitor measurement module to an input of the PA are coupledthrough the transmit block; a low noise amplifier (LNA) wherein signalscoupled between the second terminal of the loop-back circuit and thecontrol and measurement module are coupled through the LNA; and atransmit/receive (T/R) switch having a first input/output (I/O)terminal, a second I/O terminal and a common terminal, the first I/Oterminal coupled to the output of the PA, the second I/O terminalcoupled to an input of the LNA and the common terminal switchable tomake connection with either the first I/O terminal or the second I/Oterminal and wherein the loop-back circuit is formed by the leakage fromthe first I/O terminal to the second I/O terminal between the output ofthe PA and the input of the LNA.
 25. The transceiver of claim 24,further comprising a receive block, wherein signals coupled between theLNA and the control and measurement module are coupled through thereceive block.
 26. The transceiver of claim 25, wherein: the receiveblock includes a digital to analog converter (DAC); the control andmeasurement module is configured to: control the gain of digital inputsto the DAC; set the gain of the digital inputs to the DAC independent ofthe PA based on a determination of whether the distortion to the signalcoupled from the output of the loop-back circuit is above an acceptablelimit, wherein: if the distortion to the signal coupled from the outputof the loop-back circuit is above the acceptable limit, gain of thedigital inputs to the DAC is decreased; and if the distortion to thesignal coupled from the output of the loop-back circuit is below theacceptable limit, gain of the digital inputs to the DAC is increased.27. The transceiver of claim 24, wherein the output of the PA is coupledto an operational load.
 28. The transceiver of claim 27, wherein theoperational load is an active network.
 29. The transceiver of claim 27,wherein the control and measurement module is configured to provide atest signal to the PA to be transmitted during times at whichtransmission of test signals will not interfere with operations of thenetwork.
 30. The transceiver of claim 27, wherein the control andmeasurement module is configured to: (i) receive information intended tobe transmitted to a receiver over the network; (ii) modulate theinformation; and (iii) couple the modulated information to the PA. 31.The transceiver of claim 24, wherein distortion measurement comprises ameasurement of the amount of amplitude compression in the peak amplitudeof a loop-back signal.
 32. The transceiver of claim 24, wherein: thetransmit block includes a pre-amplifier; the control and measurementmodule is configured to: set gain of the pre-amplifier independent ofthe PA by a determination of whether the distortion to the signalcoupled from the output of the loop-back circuit is above an acceptablelimit; if the distortion to the signal coupled from the output of theloop-back circuit is above the acceptable limit, provide a signal to thepre-amplifier to increase the gain provided by the pre-amplifier; and ifthe distortion to the signal coupled from the output of the loop-backcircuit is below the acceptable limit, reduce the gain provided by thepre-amplifier.
 33. The transceiver of claim 32, wherein the distortionmeasurement is made based on measurements of a peak amplitude of aloop-back signal.
 34. The transceiver of claim 32, wherein thedistortion measurement is made based on measurements of a peak toaverage ratio of a loop-back signal.
 35. The transceiver of claim 32,wherein the distortion measurement is made based on amplitudecompression in the peak amplitude of a loop-back signal.
 36. Thetransceiver of claim 32, wherein the distortion measurement is madebased on both phase compression and amplitude compression in the peakamplitude of a loop-back signal.
 37. The transceiver of claim 36,wherein the signal to be transmitted is a test tone.
 38. The transceiverof claim 37, wherein the test tone is an orthogonal frequency divisionmultiplexed (OFDM) signal comprising a plurality of carriers upon whichtest data is modulated.
 39. The transceiver of claim 36, wherein thesignal to be transmitted is a live transmit signal modulated withinformation intended for reception by a receiver.
 40. The transceiver ofclaim 32, wherein the distortion measurement is made based on transmitmodulation error rate (MER) for a loop-back signal.
 41. A transceivercomprising: a variable gain power amplifier (PA), the PA configured toreceive a signal to be transmitted, and provide gain to the signal to betransmitted; a loop-back circuit having a first terminal and a secondterminal, the first terminal coupled to an output of the PA; a controland measurement module that is: coupled to the PA and to an output ofthe loop-back circuit; and configured to: provide the signal to betransmitted to the PA; measure whether distortion to the signal coupledfrom the output of the loop-back circuit is above an acceptable limit,wherein distortion is measured by measuring the amount of amplitudecompression in the peak amplitude of a loop-back signal; if the amountof distortion is below the acceptable limit, provide a signal to the PAto increase the gain provided by the PA; and if the amount of distortionis above the acceptable limit, reduce the gain provided by the PA. 42.The transceiver of claim 41 further comprising: a transmit block,wherein signals coupled from the control and monitor measurement moduleto an input of the PA are coupled through the transmit block; a lownoise amplifier (LNA) wherein signals coupled between the secondterminal of the loop-back circuit and the control and measurement moduleare coupled through the LNA.
 43. The transceiver of claim 42, furthercomprising a receive block, wherein signals coupled between the LNA andthe control and measurement module are coupled through the receiveblock.
 44. The transceiver of claim 43, wherein: the receive blockincludes a digital to analog converter (DAC); the control andmeasurement module is configured to: control the gain of digital inputsto the DAC; and set the gain of the digital inputs to the DACindependent of the PA based on a determination of whether the distortionto the signal coupled from the output of the loop-back circuit is abovean acceptable limit, wherein: if the distortion to the signal coupledfrom the output of the loop-back circuit is above the acceptable limit,gain of the digital inputs to the DAC is decreased; and if thedistortion to the signal coupled from the output of the loop-backcircuit is below the acceptable limit, gain of the digital inputs to theDAC is increased.
 45. The transceiver of claim 42, wherein: the transmitblock includes a pre-amplifier; and the control and measurement moduleis configured to: set gain of the pre-amplifier independent of the PA bya determination of whether the distortion to the signal coupled from theoutput of the loop-back circuit is above an acceptable limit; if thedistortion to the signal coupled from the output of the loop-backcircuit is above the acceptable limit, provide a signal to thepre-amplifier to increase the gain provided by the pre-amplifier; and ifthe distortion to the signal coupled from the output of the loop-backcircuit is below the acceptable limit, reduce the gain provided by thepre-amplifier.
 46. The transceiver of claim 45, wherein the distortionmeasurement is made based on measurements of a peak amplitude of theloop-back signal.
 47. The transceiver of claim 45, wherein thedistortion measurement is made based on measurements of a peak toaverage ratio of the loop-back signal.
 48. The transceiver of claim 45,wherein the distortion measurement is made based on amplitudecompression in the peak amplitude of the loop-back signal.
 49. Thetransceiver of claim 45, wherein the distortion measurement is madebased on both phase compression and amplitude compression in the peakamplitude of the loop-back signal.
 50. The transceiver of claim 49,wherein the signal to be transmitted is a test tone.
 51. The transceiverof claim 50, wherein the test tone is an orthogonal frequency divisionmultiplexed (OFDM) signal comprising a plurality of carriers upon whichtest data is modulated.
 52. The transceiver of claim 49, wherein thesignal to be transmitted is a live transmit signal modulated withinformation intended for reception by a receiver.
 53. The transceiver ofclaim 45, wherein the distortion measurement is made based on transmitmodulation error rate (MER) for the loop-back signal.
 54. Thetransceiver of claim 41, wherein the output of the PA is coupled to anoperational load.
 55. The transceiver of claim 46, wherein anoperational load is an active network.
 56. The transceiver of claim 46,wherein the control and measurement module is configured to provide atest signal to the PA to be transmitted during times at whichtransmission of test signals will not interfere with operations of thenetwork.
 57. The transceiver of claim 46, wherein the control andmeasurement module is configured to: (i) receive information intended tobe transmitted to a receiver over the network; (ii) modulate theinformation; and (iii) couple the modulated information to the PA.
 58. Atransceiver comprising: a variable gain power amplifier (PA), the PAconfigured to receive a signal to be transmitted, and provide gain tothe signal to be transmitted; a loop-back circuit having a firstterminal and a second terminal, the first terminal coupled to an outputof the PA; a control and measurement module that is: coupled to the PAand to an output of the loop-back circuit; and configured to: providethe signal to be transmitted to the PA; measure whether distortion tothe signal coupled from the output of the loop-back circuit is above anacceptable limit; if the amount of distortion is below the acceptablelimit, provide a signal to the PA to increase the gain provided by thePA; and if the amount of distortion is above the acceptable limit,reduce the gain provided by the PA; a transmit block, wherein signalscoupled from the control and monitor measurement module to an input ofthe PA are coupled through the transmit block; and a low noise amplifier(LNA) wherein signals coupled between the second terminal of theloop-back circuit and the control and measurement module are coupledthrough the LNA, wherein: the transmit block includes a pre-amplifier;and the control and measurement module is configured to: set gain of thepre-amplifier independent of the PA by a determination of whether thedistortion to the signal coupled from the output of the loop-backcircuit is above an acceptable limit; if the distortion to the signalcoupled from the output of the loop-back circuit is above the acceptablelimit, provide a signal to the pre-amplifier to increase the gainprovided by the pre-amplifier; and if the distortion to the signalcoupled from the output of the loop-back circuit is below the acceptablelimit, reduce the gain provided by the pre-amplifier.
 59. Thetransceiver of claim 58, further comprising a receive block, whereinsignals coupled between the LNA and the control and measurement moduleare coupled through the receive block.
 60. The transceiver of claim 9,wherein: the receive block includes a digital to analog converter (DAC);the control and measurement module is configured to: control the gain ofdigital inputs to the DAC; and set the gain of the digital inputs to theDAC independent of the PA based on a determination of whether thedistortion to the signal coupled from the output of the loop-backcircuit is above an acceptable limit, wherein: if the distortion to thesignal coupled from the output of the loop-back circuit is above theacceptable limit, gain of the digital inputs to the DAC is decreased;and if the distortion to the signal coupled from the output of theloop-back circuit is below the acceptable limit, gain of the digitalinputs to the DAC is increased.
 61. The transceiver of claim 58, whereinthe output of the PA is coupled to an operational load.
 62. Thetransceiver of claim 61, wherein the operational load is an activenetwork.
 63. The transceiver of claim 61, wherein the control andmeasurement module is configured to provide a test signal to the PA tobe transmitted during times at which transmission of test signals willnot interfere with operations of the network.
 64. The transceiver ofclaim 61, wherein the control and measurement module is configured to:(i) receive information intended to be transmitted to a receiver overthe network; (ii) modulate the information; and (iii) couple themodulated information to the PA.
 65. The transceiver of claim 58,wherein the distortion measurement is made based on measurements of apeak amplitude of a loop-back signal.
 66. The transceiver of claim 58,wherein the distortion measurement is made based on measurements of apeak to average ratio of a loop-back signal.
 67. The transceiver ofclaim 58, wherein the distortion measurement is made based on amplitudecompression in the peak amplitude of a loop-back signal.
 68. Thetransceiver of claim 58, wherein the distortion measurement is madebased on both phase compression and amplitude compression in the peakamplitude of a loop-back signal.
 69. The transceiver of claim 68,wherein the signal to be transmitted is a test tone.
 70. The transceiverof claim 69, wherein the test tone is an orthogonal frequency divisionmultiplexed (OFDM) signal comprising a plurality of carriers upon whichtest data is modulated.
 71. The transceiver of claim 68, wherein livetransmit signals modulated with information intended for reception by areceiver.
 72. The transceiver of claim 58, wherein the distortionmeasurement is made based on transmit modulation error rate (MER) forthe loop-back signal.
 73. A transceiver comprising: a variable gainpower amplifier (PA), the PA configured to receive a signal to betransmitted, and provide gain to the signal to be transmitted; aloop-back circuit having a first terminal and a second terminal, thefirst terminal coupled to an output of the PA; a control and measurementmodule that is: coupled to the PA and to an output of the loop-backcircuit; and configured to: provide the signal to be transmitted to thePA; measure whether distortion to the signal coupled from the output ofthe loop-back circuit is above an acceptable limit; if the amount ofdistortion is below the acceptable limit, provide a signal to the PA toincrease the gain provided by the PA; and if the amount of distortion isabove the acceptable limit, reduce the gain provided by the PA; atransmit block, wherein signals coupled from the control and monitormeasurement module to an input of the PA are coupled through thetransmit block; a low noise amplifier (LNA) wherein signals coupledbetween the second terminal of the loop-back circuit and the control andmeasurement module are coupled through the LNA; and a receive block,wherein signals coupled between the LNA and the control and measurementmodule are coupled through the receive block, wherein: the receive blockincludes a digital to analog converter (DAC); and the control andmeasurement module is configured to: control the gain of digital inputsto the DAC; and set the gain of the digital inputs to the DACindependent of the PA based on a determination of whether the distortionto the signal coupled from the output of the loop-back circuit is abovean acceptable limit, wherein: if the distortion to the signal coupledfrom the output of the loop-back circuit is above the acceptable limit,gain of the digital inputs to the DAC is decreased; and if thedistortion to the signal coupled from the output of the loop-backcircuit is below the acceptable limit, gain of the digital inputs to theDAC is increased.
 74. The transceiver of claim 73, wherein the output ofthe PA is coupled to an operational load.
 75. The transceiver of claim74, wherein the operational load is an active network.
 76. Thetransceiver of claim 74, wherein the control and measurement module isconfigured to provide a test signal to the PA to be transmitted duringtimes at which transmission of test signals will not interfere withoperations of the network.
 77. The transceiver of claim 74, wherein thecontrol and measurement module is configured to: (i) receive informationintended to be transmitted to a receiver over the network; (ii) modulatethe information; and (iii) couple the modulated information to the PA.